1. Field of the Invention
The present invention generally relates to tensioners and, more particularly, to tensioners for band saw cutting blades and the like.
2. Brief Description of the Prior Art
As shown in FIG. 1, band saws A generally include a frame B, a first pulley shroud C connected to the frame B, a manually rotatable tensioner, such as a screw-type tensioner D, removably and slideably attached to the frame B by slots E, a first pulley F (shown in phantom) rotatably attached to the screw-type tensioner D, a second pulley G (shown in phantom) lying in the same plane as the first pulley F and rotatably attached to the frame B, a second pulley shroud H connected to the frame B, a continuous cutting blade I attached to the first pulley F and the second pulley G, a blade guide attachment bar J, and a motor O connected to the second pulley G.
In normal operation, the cutting blade I must be tensioned to make the cutting blade I taut. Conversely, when the cutting blade I is worn or replacement is desired, the cutting blade I must be detensioned so that the cutting blade I can be removed from the first and second pulleys F,G.
Tensioning the cutting blade I is normally accomplished by positioning the cutting blade I on the first and second pulleys F,G and then moving the first pulley F, which lies in substantially the same plane as the second pulley G, directly away from the second pulley G. Detensioning is accomplished by moving the first pulley F toward the second pulley G. Movement of the first pulley F is facilitated by the screw-type tensioner D shown in FIG. 1. As shown in FIG. 2, the screw-type tensioner D includes a tension body K that receives, usually in a common thread arrangement, a rotatable shaft L. The tension body K is fitted into the slots E formed by the frame B so that the tension body K is moveable with respect to the frame B, as illustrated by the arrows Y1 and Y2. The tension body K further includes a shaft N that receives the first pulley F shown in FIG. 1.
With continuing reference to FIG. 2, a first end M of the rotatable shaft L contacts the frame B, so that when the rotatable shaft L is rotated in a tightening direction, shown by arrow Z1, the tension body K and the first pulley F move in the Y1 direction. This tightens the cutting blade I. When the rotatable shaft L is rotated in a loosening direction, shown by arrow Z2, the tension body K and the first pulley F move in the Y2 direction. This creates slack in the cutting blade I.
Another type of manually rotatable tensioner is disclosed in U.S. Pat. No. 769,497 to Seymour (hereinafter xe2x80x9cthe Seymour patentxe2x80x9d). The Seymour patent discloses a tensioner having a rack and pinion arrangement actuated by a rotatable handwheel.
One drawback of the prior art manually rotatable tensioners, such as the screw-type and the handwheel-type discussed above, is that they are rotated incrementally by hand. Therefore, each time the cutting blade is retensioned, the correct number of turns of the rotatable shaft L or the handwheel must be approximated. This involves a process of trial and error, which is inaccurate and time consuming.
To help eliminate some of the drawbacks of the prior art rotatable tensioners, it is an object of the present invention to provide a tensioner which is easily operated and does not require significant amounts of trial and error manipulation during retensioning of the cutting blade.
The present invention generally includes a method and apparatus for tensioning a belt, saw blade, or other continuous loop. One method to adjust the tension of a cutting blade installed on a band saw having a frame, a manually rotatable tensioner positioned adjacent to the frame, a first pulley rotatably connected to the manually rotatable tensioner, a second pulley spaced away from the first pulley, and a cutting blade strung between the first pulley and the second pulley includes the step of positioning an adjustable body between the manually rotatable tensioner and the second pulley. This step is followed by one or more of the following steps, including extending the adjustable body in a direction away from the second pulley and toward the manually rotatable tensioner so that the manually rotatable tensioner and the first pulley move in direction away from the second pulley or withdrawing the adjustable body in a direction toward the second pulley so that the manually rotatable tensioner and the first pulley move in a direction toward the second pulley. The adjustable body is preferably a rack, and the manually rotatable tensioner is preferably a screw-type tensioner having a manually rotatable shaft with opposing ends. Additional steps may include positioning the rack adjacent to an opposing end of the manually rotatable shaft, extending the rack in a direction away from the second pulley to tension the cutting blade, and withdrawing the rack in a direction toward the second pulley to detension the cutting blade.
Another method to adjust the tension of a cutting blade installed on a band saw having a frame, a screw-type tensioner positioned adjacent to the frame, the screw-type tensioner having a rotatable shaft with opposing ends, a first pulley rotatably connected to the screw-type tensioner, and a second pulley spaced away from the first pulley generally includes the steps of positioning a rack and a rotatable pinion gear between the screw-type tensioner and the second pulley, wherein the rack and pinion gear are connected by an intermeshed relationship, and the rack is movable by the pinion gear, extending the rack in a direction away from the second pulley to tension the cutting blade, and withdrawing the rack in a direction toward the second pulley to detension the cutting blade.
A band saw according to the present invention generally includes a frame having a motor connected to the frame, a first pulley and a second pulley, with the first pulley rotatably connected to the manually rotatable tensioner and the second pulley rotatably connected to the motor, a pull-type tensioner positioned between the manually rotatable tensioner and the second pulley, and a cutting blade strung between the first pulley and the second pulley. The manually rotatable tensioner is preferably a screw-type tensioner. The pull-type tensioner may include a mount defining a pivot shaft receiving orifice, a pivot shaft received in the pivot shaft receiving orifice, the pivot shaft having a first end and a second opposite end, a pinion gear positioned adjacent to the first end of the shaft, a handle positioned adjacent to the second opposite end of the shaft, and a rack connected by an intermeshed tooth relationship with the pinion gear. In operation, the handle is rotated in a first direction with respect to the mount, and the pinion gear acts to extend the rack in a direction away from the mount. When the handle is rotated in a second direction, opposite to the first direction, the pinion gear acts to withdraw the rack in a direction toward the mount.
These and other features of the present invention will be clarified in the Detailed Description of the Preferred Embodiments taken together with the attached drawings in which like reference numerals represent like elements throughout.